Work Towards the Near Real-Time Attribution of Extreme Weather and Climate Events at the German Weather Service (Deutscher Wetterdienst)

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Jordis Tradowsky1,2, Philip Lorenz1, Frank Kreienkamp1 and Amalie Skålevåg1 ¹Deutscher Wetterdienst, ²Bodeker Scientific

28.04.2021 Dr. Jordis Tradowsky, DWD, Regionales Klimabüro Potsdam Outline of the presentation

• Motivation - Why Deutscher Wetterdienst works towards near real-time attribution of extreme weather events • Overview and goals of the ClimXtreme project B1.2 • How should the attribution system under development work? Presentation of methods • Current status and outlook of the ClimXtreme project B1.2 • Other attribution projects currently underway at Deutscher Wetterdienst

28.04.2021 Dr. Jordis Tradowsky, DWD, Regionales Klimabüro Potsdam 2 Why Deutscher Wetterdienst works towards near real-time attribution of extreme weather events

• The science of extreme event attribution has developed quickly in the last decade and many attribution studies are available in the scientific literature. • However, the wider public is interested in attribution statements within days after an extreme event. • This is why an operational attribution system is required! Figure 1: Flood of the Isar in June 2013 © Renate Poßiel / Deutscher Wetterdienst.

28.04.2021 Dr. Jordis Tradowsky, DWD, Regionales Klimabüro Potsdam 3 ClimXtreme project B1.2 „Attribution of weather and climate extremes with focus on Germany including preparatory work for operationalisation”

• This project is part of the larger ClimXtreme research network on extreme events in the context of climate change. • Main goal of the project: A largely automated work flow for the extreme event attribution. • Focus is on heat waves, droughts and large- scale precipitation events. Figure 2: Rain, heat and drought © Hanna Luca

28.04.2021 Dr. Jordis Tradowsky, DWD, Regionales Klimabüro Potsdam 4 Goals of ClimXtreme project B1.2

• Develop a work flow for the attribution of extreme weather and climate events. • Operationalise the analysis where possible to provide attribution statements in the immediate aftermath of an extreme event. • Evaluate existing approaches for event attribution and their suitability for operationalisation. • Evaluate the suitability of existing datasets for the attribution of extreme events in Germany. • Work closely with other ClimXtreme projects such as B1.1 (Advanced Detection and Attribution) to develop new methods were required.

28.04.2021 Dr. Jordis Tradowsky, DWD, Regionales Klimabüro Potsdam 5 Approaches for event attribution studies using climate model simulation

• A variety of approaches can be used in Figure 3: Important steps in an attribution system probabilistic attribution studies. These approaches are typically based on climate model simulations as well as on observations and follow the general steps of Figure 3. • The attribution methods that are taken into account within ClimXtreme B1.2 are: • Comparison of factual and counter- factual simulations • Comparison of different time frames • Bayesian attribution

28.04.2021 Dr. Jordis Tradowsky, DWD, Regionales Klimabüro Potsdam 6 Comparison of factual and counter-factual simulations

• Probabilistic attribution using climate model simulations under nowadays (factual, historical) and naturalised (counter-factual, historicalnatural) conditions. • Analysing the shift in probabilities of a given event occurring under the factual and counter-factual scenario. • This method can evaluate changes in the intensity and severity of extreme events that are represented by the Figure 4: The world under anthropogenic influence (factual, model. left), world without anthropogenic influence (counter-factual, right). © Hanna Luca

28.04.2021 Dr. Jordis Tradowsky, DWD, Regionales Klimabüro Potsdam 7 Comparison of different time frames

• As there are not that many counter-factual (histnat) simulations available, we will also look into comparing different time frames from climate model simulations, i.e. • Compare a 30-year period in the past with the most current 30 years. • Compare a current 30-year period with a 30-year period in the future (under a selected climate scenario). • This comparison uses similar methods as applied in the comparison of factual and counter-factual simulations. • It analyses changes in the severity and frequency of events that are represented by the underlying climate models.

28.04.2021 Dr. Jordis Tradowsky, DWD, Regionales Klimabüro Potsdam 8 Bayesian attribution

• In close collaboration with ClimXtreme project B1.1 (A. Hense, I. Pscheidt, C. Ohlwein; University of Bonn), we will work on the attribution using Bayesian methods. • Within Bayesian detection and attribution, the questions posed are: • Detection: Given the observations, what is the conditional probability of the analysed hist and histnat climate model simulations, respectively. • Attribution: Given the hist and histnat simulations respectively, what is the conditional probability of the observations to occur.

28.04.2021 Dr. Jordis Tradowsky, DWD, Regionales Klimabüro Potsdam 9 Current status ClimXtreme B1.2 Outlook ClimXtreme B1.2

• Work on this project has started in • Project will end in February 2023. October 2020. • Goal is to have a semi-automated • We are developing the attribution system in place and tested. system in python. Currently not all • DWD aims to provide attribution steps are implemented, but we are statements to the interested adding more steps and improving the population on a more regular basis. existing steps throughout the project.  This project will support this goal! • We need to develop a methodology to combine the results from different models and potentially different methods.

28.04.2021 Dr. Jordis Tradowsky, DWD, Regionales Klimabüro Potsdam 10 Other attribution projects currently underway at DWD

Copernicus „Prototype extreme event and attribution service“ • Copernicus project in collaboration with Royal Netherlands Meteorological Institute, Oxford University, MeteoFrance, UK Met Office, DWD, Netherlands e-science Center • Development of a prototype event attribution service that follows an eight step protocol outlined by Philip et al., 2020. • Several test studies have been performed by the project team to date.

28.04.2021 Dr. Jordis Tradowsky, DWD, Regionales Klimabüro Potsdam 11 Thank you very much for your attention!

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28.04.2021 Dr. Jordis Tradowsky, DWD, Regionales Klimabüro Potsdam 12